Papaya Plant Major Pests, Diseases and Weeds

Papaya Pests and Diseases

Papaya plant Major Pests

• Papaya Fruit Fly (Toxotrypana curvicauda): The larvae of this fly devour papaya seeds and their interior tissues. Particularly menacing is the wasp-like papaya fruit fly, as it lays eggs on the fruit, leading to a larval infestation. Only thick-fleshed fruits are somewhat spared from this onslaught. Controlling this pest at a commercial scale remains a formidable challenge. Home gardeners resort to covering the fruit with paper bags, but this must be done early, replacing the bags every 10 days or 2 weeks as the fruits mature. This pest can cause significant economic losses in papaya farming. The key to controlling papaya fruit flies is to prevent the egg-laying in fruits. Controlling adult females before they deposit eggs in the fruit is necessary. Bagging can effectively control the fruit fly in small plantings (one to 25 plants or less than 1/10 hectare).
• Papaya Webworm (Homolapalpia dalera): This cunning culprit weaves a web around the fruit and stem, feasting on the tissue beneath. It hides between the main stem and the fruits, damaging both and making them susceptible to diseases like anthracnose. Swift action is essential – spray at the onset of fruit formation or at the first sign of webs. These webs can act as entry points for other pathogens, further jeopardizing papaya crops. To manage this issue, it is advised to use an insecticid based on the advice of your regional agronomist. Additionally, employing malathion and/or Bacillus thuringiensis for other insects could potentially decrease or assist in controlling the webworms.
• Papaya White Fly (Trialeuroides variabilis): These sap-sucking insects target the underside of younger leaves, draining the plant’s nutrients. An infestation often leads to the growth of black mildew, fed by the whitefly’s excretions. Timely intervention is crucial; commence spraying or dusting when you observe a significant number of adults. Neglecting this pest can severely impact papaya plant health and overall yield. The whiteflies in papaya are parasitized by Amitus fuscipennis, Amitus sp. and Encarsia tabacivora.
• Red Spider Mite: This mite sucks juices from the leaves and commonly infests the stem and leaves, scarring the fruit. Young plants, especially in cooler weather, are at risk of damage from the broad mite. Vigilance is the key to early detection. Left unchecked, red spider mites can defoliate papaya plants, reducing photosynthesis and fruit production.
• Scale Insects: Scale insects, such as Aspidiotus destructor, Coccus hesperidium, and Philaphedra sp., can infest papayas plant and fruit might even be more susceptible. Proactive measures are essential to prevent the disfigurement and loss of papaya fruit quality. These pests can also transmit diseases, compounding the damage. This scale insect can be controlled from a diverse range of at least nine predators, including the mealy bug ladybird (Cryptolaemus montrouzieri). It is also susceptible to attack by the Verticillium lecanii fungus, which can lead to mortality rates of up to 90% during the summer. Additionally, two small parasitic wasps, namely Coccophagous lycimnia and Trichomastus portoricensis, intermittently contribute to significant mortality levels.
• Nematodes: Root-knot nematodes like Meloidogyne incognita acrita and reniform nematodes Rotylenchulus reniformis, pose a substantial threat, particularly in sandy soils. Effective chemical control is challenging and costly, so preventive actions like site rotation, maintaining plant vigor, and mulching are essential. Soil fumigation may be necessary if nematode populations are high. Nematodes can undermine the root system, stunting plant growth and reducing fruit production.
• Gophers: Gophers are another menace, burrowing underground and feeding on the roots of papaya plants. Their activity can lead to severe damage and even plant loss. However, they can be deterred by planting in wire baskets. Gophers can undermine the stability and health of papaya plants, making protective measures crucial.

Most Important Diseases of Papaya Plant 

The disease with the higher economic importance is is caused by the mosaic virus, which is transmitted mechanically or by the green peach aphid and other aphids, including the green citrus aphid, Aphis spiraecola. Virus mosaics have no remedy, but measures to avoid spread include destroying affected plants, controlling aphids with pesticides, and eliminating all members of the Cucurbitaceae from the vicinity. Mosaic is sporadic and scattered. A serious disease during the seedling stage is seedling rot or Phytophthora, causing soft rot and wilting of seedlings, which also affects mature trees. It can be controlled by good drainage and sanitation control, that is, by removing all infected plants. Anthracnose causes dark, depressed lesions on ripe fruits, which then become soft, dark-colored and unattractive. The fungus Collectotrichum gloeosperoides can be controlled by recommended fungicides. The root-knot nematode affects the roots, causing galls and damage to the root system. 

• Papaya Ringspot Virus (PRSV): This virus is very common and spreads through the same carriers. Mosaic and ringspot viruses are the main issues affecting papaya production and the biggest threats to the papaya industry. Early signs include irregular patterns on young leaves, yellowing with transparent areas, leaf distortion, and ring-shaped marks on the fruit. If you don’t remove infected plants, the disease can quickly spread across the plantation. Fruits that develop two to three months after the first symptoms appear will have an unpleasant, bitter taste. It’s believed that at least three virus diseases are contributing to papaya decline in East Africa, and it’s suggested that these diseases may be partly spread when tapping green fruits for their latex, which is the source of papain. There are no control measures for this disease, and it is very difficult to control it once it has become established. Therefore the farmer should focus on preventive measures to avoid infestation. Infected plants should be removed and destroyed as soon as the symptoms are noticed.
• Bunchy Top: It’s transmitted by leafhoppers like Empoasca pawpawe, E. dilitara, and E. stevensi. Papaya plants can experience die-back, a condition of unknown origin. It starts with the shortening of the petioles and bunching of inner crown leaves. Then, larger crown leaves quickly turn yellow. You can manage this by cutting back affected plants at the first sign of the disease. If you cover the cut stem to prevent rotting, healthy side branches will grow back. This problem is most common during hot, dry springs following a season of heavy rains. Antibiotics, such as chlortetracycline or tetracycline hydrochloride, have successfully treated Bunchy Top disease in the soil around infected plants.
• Anthracnose: This is a significant papaya disease caused by the fungus Colletotrichum gloeosporioides. It primarily affects ripe fruits, causing rot. You can control it by regular spraying and hot water treatment of harvested fruits. Some strains of this fungus cause “chocolate spots,” which are small, angular, superficial lesions. A disease similar to anthracnose, attacking ripening papayas, was reported in the Philippines in 1974, with the causal agent identified as Fusarium solani. . It can be controlled by spraying Dithane M-45 (a broad spectrum fungicide that is composed of Ethylene-bis-dithio-carbamate %, manganese 16 %, and Zinc 2 %) on the leaves and fruits every ten days. Of course, you should always ask for advice from your regional agronomist and apply fungicides available in your region.
• Phytophthora Blight: This disease is prevalent in wet weather. Phytophthora parasitica affects and rots the stem, roots, and fruit, leading to fruit fall and mummification. You can reduce its incidence by using fungicidal sprays (e.g metalaxyl-M) to soil and removing diseased plants and fruits.
• Root Rot: Pythium sp. causes severe root rot in papayas in Africa. P. ultimum causes trunk rot. Collar rot in 8- to 10-month-old seedlings, evidenced by stunting, leaf yellowing and shedding, and total root loss is attributed to attack by Calonectria sp. Sometimes, root rot is so severe in India that growers abandon their plantations.
• Powdery Mildew: Papaya plants and their fruits are often affected by powdery mildew caused by Oidium caricae. Remove infected plants as soon as these are detected. Regular inspection and rogueing can contain the disease in many instances. Wettable sulfur, sulfur dust, or lime sulfur, along with potassium bicarbonate, have demonstrated efficacy in managing this disease. It is essential to note that these treatments may pose a risk of plant toxicity when administered in hot weather conditions. Alternatively, baking powder, neem oil extracts, and soap solutions might be beneficial in certain instances.
• Fruit Rot: Injured fruits are susceptible to fungal rot caused by R. stolonifer and Phytophthora palmivora. Stem-end rot occurs when fruits are pulled instead of cut from the plant. This fungus spreads quickly through the wounds. Research shws that the application of Reforce® + salicylic acid to 6 days before the harvest was efficient in the control of the disease and delayed ripening of the fruit. The application of Acibenzolar-S-Methyl after harvest (0.15; 0.30 g/L) was effective against fruit rot. Always ask your regional agronomists about what products are available in the region. Additionally, apply only authorized products for papaya to avoid any residues in your fruits.

Physiological and Physical Disorders in Papaya Plants

Like all fruits, Papayas are susceptible to various physiological and physical disorders. These issues can affect the fruit’s appearance, taste, and quality. 

• Blossom End Rot: This disorder is caused by a calcium deficiency in the fruit. It appears as a dark, leathery patch on the blossom end of the papaya. To prevent this, ensure the plant receives adequate calcium through proper fertilization.
• Skin Scarring: Papayas can develop scars on their skin due to wind damage, abrasions, or insect feeding. While these scars don’t affect the fruit’s taste, they reduce its visual appeal.
• Sunburn: Excessive exposure to direct sunlight can lead to sunburn on papaya skin. Sunburned areas become discolored and leathery. Protecting the fruits with shading or pruning the plant for better fruit coverage can help prevent sunburn.
• Chilling Injury: Papayas are sensitive to low temperatures. Exposure to cold conditions, even for a short period, can cause chilling injury. Symptoms include surface pitting, uneven ripening, and off-flavors. Store papayas above 50°F (10°C) to avoid chilling injury.
• Internal Browning: This disorder manifests as brown or translucent patches inside the papaya. It’s usually caused by calcium deficiencies, temperature fluctuations, or moisture stress during fruit development. Adequate irrigation and stable temperatures can help prevent internal browning.

Weed control in a papaya plantation

The most important and common weeds in papaya are:

• Cyanodan dactylon
• Cyperus rotundus – (Nutgrass)
• Ageratum conyzoides – (Gog weed)
• Amaranthus viridis
• Boerhaevia diffusa 
• Euphorbia hirta 
• Parthenium hysterophorus 
• Trianthema decanni
• Trianthema portulacastrum 

Either mechanical or chemical methods can succeed in weed control. Manage papaya weeds through either manual (mechanical) or chemical means. For optimal weed control, consider employing a combination of both approaches. Mulching is highly effective in suppressing weed growth while preserving soil moisture; apply mulch, especially in young plantings, using grasses like Guatemala, Napier, or other plant materials. Mechanical methods employ 2 types of either hand or mechanical slashing: Care should be taken when hand slashing is used not to cause injuries to the tree trunk. Continuous mechanical slashing may lead to compaction, and ripping may have to be considered to promote root growth. Plowing displaces the compacted layer to just below the depth of the plow while ripping can break up compacted layers if it is done when the soil is relatively hard and dry.  In papaya orchards, only paraquat and glyphosate among pre and post-emergence herbicides have been reported for use. Be cautious to prevent the spray solution from drifting onto young seedlings.

For Further reading

Papaya Interesting facts, Nutritional value, and Health benefits

Papaya plant information

Papaya Soil Preparation, Planting, and Plant density

Papaya propagation and Pollination

Papaya Plant Care – Irrigation and Fertilization of Papaya plants

How to cultivate papayas for profit – Complete papaya production guide

Papaya Plant Major Pests, Diseases and Weed Management

Papaya Harvest,  Yield and Storage

Papaya Handling, Grading, and Packing

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